In the case where a thin film is formed on a substrate, a sputtering system in which a thin film is formed on a substrate by the sputtering technique has conventionally been used. Generally, the sputtering system forms a thin film on one side of a substrate by the sputtering technique. However, a sputtering system in which targets are placed so as to face both surfaces of a substrate and a thin film is formed on both surfaces of substrate by the sputtering technique has also been proposed (for example, refer to Patent Document 1).    Patent Document 1: Japanese Patent Laid-Open No. 5-295538 (FIG. 1)
In the conventional sputtering system (film forming apparatus) described in Patent Document 1, when a substrate subjected to double-side film forming is transported out of a vacuum vessel (film forming chamber) and when an untreated substrate is transported into the vacuum vessel (film forming chamber), it is necessary to exhaust the vacuum vessel to control the pressure therein to a predetermined value by opening the vacuum vessel to the atmosphere before an untreated substrate is transported into the vacuum vessel and a double-side film forming process is performed, so that double-side film forming cannot be carried out continuously with high efficiency.
Also, in the sputtering system (film forming apparatus) capable of carrying out double-side film forming as described in Patent Document 1, in order to obtain a high-quality thin film, it is necessary to prevent the temperature of substrate from being raised to a predetermined value or higher by plasma generating at the time of film forming or by radiation heat from the cathode. However, it is difficult to provide a cooling means on the substrate because a film is formed on both surfaces of the substrate.
Accordingly, an object of the present invention is to provide a film forming apparatus which is capable of forming a high-quality film on both surfaces of a substrate by sputtering continuously with high efficiency by restraining a rise in temperature of the substrate to a predetermined value or higher.